The subject matter of this disclosure relates generally to high speed semiconductor switches, and more particularly a coaxial power module that reduces electromagnetic interference (EMI) caused by high speed semiconductor switching.
More high power wide bandgap semiconductors, such as the silicon carbide (SiC) metal oxide semiconductor field-effect transistor (MOSFET) are becoming commercially available to the power conversion industry. These devices have high switching speeds and high temperature capabilities making them ideal for usage in high frequency and high-end applications such as military and avionics. Such applications are very sensitive to radiated and conducted electrical noise. Since these new semiconductors are switched with such high speeds, the interconnections and the packaging implementations of these functional blocks could be a source for both radiated and conducted electrical energy that can disrupt sensitive control and communications equipment.
Commercial power semiconductor modules historically have been designed to replicate an industry standard package so as to be able to replace existing field-installed devices. The foregoing approach is no longer a viable solution with the onset of new faster switching and high temperature technology. Existing industry standard packages have inherent geometries that are not conducive to implementing tight power interconnection. Many approaches have been implemented in attempts to reduce inductance using local planar interconnecting bus work within a module. None of these approaches have carried the concept down to the die level interconnections. Recent attempts at reducing inductance within a module have resulted in large conduction loops formed by the wire-bonds and associated routing strategies. Further, modules have been attached to DC bus bars using rectangular power contacts separated by large spaces and having to be bolted on to the bus bars themselves, creating additional interconnection inductances, and thus negate whatever gains are made by internal planar interconnections inside the power module. Modules bolted to bus bars disadvantageously take up large spaces making it difficult to design very tightly connected high-density converter/inverter modules for high-end applications such as avionics or defense related designs.
In view of the foregoing, there is a need for a technique to reduce EMI caused by high power, high speed semiconductor switches to a level that will not cause interference with sensitive control and communications equipment that either employs high power, high speed semiconductor switches or that is in the immediate vicinity of such high power, high speed semiconductor switches. The technique would be particularly advantageous if it could be applied to provide a structure having a cylindrical geometry that is conducive to the mounting of power semiconductor modules, for example, in motor rotor or stator or missile cases.